Light source modules are most widely used in illumination systems which have a variety of applications, including projection displays, backlights for liquid crystal displays (LCDs) and others. Projection systems usually include a source of light, illumination optics, an image-forming device, projection optics and a projection screen. The illumination optics collect light from a light source and direct it to one or more image-forming devices in a predetermined manner. The image-forming devices, controlled by an electronically conditioned and processed digital video signal, produce an image corresponding to the video signal. Projection optics then magnify the image and project it onto the projection screen. White light sources, such as arc lamps, in conjunction with color wheels have been and still are predominantly used as light sources for projection display systems. However, recently, light emitting diodes (LEDs) were introduced as an alternative due to their longer lifetime, higher efficiency and superior thermal characteristics.
LEDs typically include an LED die or chip mounted on a metal header. The header can have a reflective cup in which the LED die is mounted, and electrical leads connected to the LED die. Some packages may also include a molded transparent resin that encapsulates the LED die. The encapsulating resin can have either a nominally hemispherical front surface to partially collimate light emitted from the die, or a nominally flat surface. Moreover, an optical element may be brought into contact or close proximity with a surface of an LED die to couple or “extract” light therefrom in order to reduce the amount of light trapped within the die.
Also, extraction structures can be formed or positioned on the LED emitter to help couple light out of the LED die, thereby preventing the light from being trapped therein and wasted. For example, roughening the emitting surface of the LED die or providing a large number of facets or other structures on such surface, such as sub-wavelength structure, can be used to enhance light extraction from the LED die. Other extraction structures include high extraction photonic crystal structures and wire grid extraction components. Still other extraction structures include glass or ceramic extractors or extractor arrays as disclosed in U.S. Patent Application Publications US2006/0091411 (Ouderkirk et al.) “High Brightness LED Package”, US2006/0091798 (Ouderkirk et al.) “High Brightness LED Package With Compound Optical Element(s)”, and US2006/0092532 (Ouderkirk et al.) “High Brightness LED Package With Multiple Optical Elements”, all incorporated herein by reference.
Recent advances in solid state lighting, optics, and display elements are allowing the creation of extremely small, full-color projectors. In order to make these color projectors small enough to be incorporated into a cell phone, it is necessary to explore very efficient and compact means of combining colors. There are two predominant methods of creating color projection. The first method, known as “Color-Sequential,” uses a dichroic X-cube to overlay light from individual red, green and blue light sources and image these colors onto a monochrome microdisplay in a specific time-sequential fashion. The second method, known as “Color-Filtering,” entails imaging a white light source onto a microdisplay with red/green/blue color filters.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.